Not applicable.
Investigators in the electric motor arts have been called upon to significantly expand motor technology from its somewhat static status of many decades. Improved motor performance particularly has been called for in such technical venues as computer design and secondary motorized systems carried by vehicles, for example, in the automotive and aircraft fields. With progress in these fields, classically designed electric motors, for example, utilizing brush-based commutation, have been found to be unacceptable or, at best, marginal performers.
From the time of its early formation, the computer industry has employed brushless d.c. motors for its magnetic memory systems. The electric motors initially utilized for these drives were relatively expensive and incorporated a variety of refinements particularly necessitated with the introduction of rotating disc memory. Over the recent past, the computer industry has called for very low profile motors capable of performing in conjunction with very small disc systems and at substantially elevated speeds.
Petersen, in U.S. Pat. No. 4,745,345, entitled xe2x80x9cD.C. Motor with Axially Disposed Working Flux Gapxe2x80x9d, issued May 17, 1988, describes a PM d.c. motor of a brushless variety employing a rotor-stator pole architecture wherein the working flux gap is disposed xe2x80x9caxiallyxe2x80x9d with the transfer of flux being in parallel with the axis of rotation of the motor. This xe2x80x9caxialxe2x80x9d architecture further employs the use of field windings which are simply structured, being supported from stator pole core members, which, in turn, are mounted upon a magnetically permeable base. The windings positioned over the stator pole core members advantageously may be developed upon simple bobbins insertable over the upstanding pole core members. Such axial type motors have exhibited excellent dynamic performance and, ideally, may be designed to assume very small and desirably variable configurations.
Petersen in U.S. Pat. No. 4,949,000, entitled xe2x80x9cD.C. Motorxe2x80x9d, issued Aug. 14, 1990 describes a d.c. motor for computer applications with an axial magnetic architecture wherein the axial forces which are induced by the permanent magnet based rotor are substantially eliminated through the employment of axially polarized rotor magnets in a shear form of flux transfer relationship with the steel core components of the stator poles. The dynamic tangentially directed vector force output (torque) of the resultant motor is highly regular or smooth lending such motor designs to numerous high level technological applications such as computer disc drives which require both design flexibility, volumetric efficiency, low audible noise, and a very smooth torque output.
Petersen et al, in U.S. Pat. No. 4,837,474 entitled xe2x80x9cD.C. Motorxe2x80x9d, issued Jun. 6, 1989, describes a brushless PM d.c. motor in which the permanent magnets thereof are provided as arcuate rings which rotate about a circular locus of core component defining pole assemblies. The paired permanent magnet rings are magnetized in a radial polar sense and interact without back iron in radial fashion with three core components of each pole assembly which include a centrally disposed core component extending within a channel between the magnet pairs and to adjacently inwardly and outwardly disposed core components also interacting with the permanent magnet radially disposed surface. With the arrangement, localized rotor balancing is achieved and, additionally, discrete or localized magnetic circuits are developed with respect to the association of each permanent magnet pair with the pole assembly.
Petersen in U.S. Pat. No. 5,659,217, issued Aug. 19, 1997 and entitled xe2x80x9cPermanent Magnet D.C. Motor Having Radially-Disposed Working Flux-Gapxe2x80x9d describes a PM d.c. brushless motor which is producible at practical cost levels commensurate with the incorporation of the motors into products intended for the consumer marketplace. These motors exhibit a highly desirable heat dissipation characteristic and provide improved torque output in consequence of a relatively high ratio of the radius from the motor axis to its working gap with respect to the corresponding radius to the motors"" outer periphery. The torque performance is achieved with the design even though lower cost or, lower energy product permanent magnets may be employed with the motors. See also: Petersen, U.S. Pat. No. 5,874,796, issued Feb. 23, 1999.
Over the years of development of what may be referred to as the Petersen motor technology, greatly improved motor design flexibility has been realized. Designers of a broad variety of motor driven products including household implements and appliances, tools, pumps, fans and the like as well as more complex systems such as disc drives now are afforded an expanded configuration flexibility utilizing the new brushless motor systems. No longer are such designers limited to the essentially xe2x80x9coff-the-shelfxe2x80x9d motor varieties as listed in the catalogues of motor manufacturers. Now, motor designs may become integral components of and compliment the product itself in an expanded system design approach.
During the recent past, considerable interest has been manifested by motor designers in the utilization of magnetically xe2x80x9csoftxe2x80x9d processed ferromagnetic particles in conjunction with pressed powder technology as a substitute for the conventional laminar steel core components of motors. So structured, when utilized as a motor stator core component, the product can exhibit very low eddy current loss which represents a highly desirable feature, particularly as higher motor speeds and resultant core switching speeds are called for. As a further advantage, for example, in the control of cost, the pressed powder assemblies may be net shaped wherein many intermediate manufacturing steps and quality considerations are avoided. Also, tooling costs associated with this pressed powder fabrication are substantially lower as compared with the corresponding tooling required for typical laminated steel fabrication. The desirable net shaping pressing approach provides a resultant structurally rigid magnetic particle structure that is 3-dimensional magnetically (isotropic) and avoids the difficulties encountered in the somewhat two-dimensional magnetic structure world of laminations. See generally U.S. Pat. No. 5,874,796 (supra) and U.S. Pat. No. 6,441,530.
The above-discussed PM D.C. motors achieve their quite efficient and desirable performance in conjunction with a multiphase-based rotational control. This term xe2x80x9cmultiphasexe2x80x9d is intended to mean at least a three step commutation sequence in conjunction with either a unipolar or bipolar stator coil excitation. Identification of these phases in conjunction with rotor position to derive a necessary controlling sequence of phase transitions traditionally has been carried out with two or more rotor position sensors. By contrast, simple, time domain-based multiphase switching has been considered to be unreliable and impractical since the rotation of the rotor varies in terms of speed under load as well as in consequence of a variety of environmental conditions.
The multiphase motors may be described, for instance, by arbitrarily designating the commutation phase sequence of a three-phase motor as: A, B, and C. During those phases, a three-phase unipolar motor control must determine rotor position information for establishing the transitions from phase A to phase B to phase C to phase A as the sequence continues. Such control has been considered to require three rotor position sensors. The most typical of the position sensors are Hall devices and optical sensors. Somewhat costlier control also can be achieved with a back EMF circuit monitoring approach which eliminates all physical position sensors.
Still higher efficiencies are achieved with a three-phase bipolar motor wherein such commutation phase sequencing arbitrarily may be designated as calling for transitions from phase AB to phase AC, to phase BC to phase BA, to phase CA, to phase CB, to phase AB as the sequence continues. Here again, a practical control for such motor architecture has been considered to require three rotor position sensors. Four-phase motors with an arbitrarily designated commutation sequence of A, B, C and D are considered to require two rotor position sensors.
While the stator architecture and pressed powder implementation of the above-discussed motors has not only substantially enhanced their practically and has lowered their structural cost, further, quite substantial cost improvements can be realized by limiting the number of bi-state rotor position sensors required for multiphase motors to only one such sensor. In this regard, currently, the multiple sensors must be positioned in substantially spaced apart locations with respect to the rotor or some slave form of sensing structuring. Thus, the significant cost advantages associated with the integration of the positional sensor and the control circuit in a single chip is lost. The resultant cost factor generally precludes the use of efficient multiphase motors with very low cost applications such as electrical circuit cooling fans. However, as the era of electronic-based systems expands, battery-based power limitations are setting the stage for much higher motor efficiency requirements. Those higher efficiencies only are available with multiphase motors. Higher efficiencies for fan motors may be required, for example, for utilization with a rapidly expanding development of laptop computers. The technology long associated with electronic circuit, low load cooling fans has been somewhat static. Usually implemented as D.C. PM devices, the motors have been structured with a single phase or xe2x80x9ctwo-pulsexe2x80x9d architecture in order to retain a capability for operation with a single sensor. Such phasing is highly inefficient, the motors necessarily experiencing zero torque based commutation switching.
In co-pending application for United States patent, Ser. No. 10/706,412 entitled xe2x80x9cMultiphase Motors With Single Point Sensing Based Commutationxe2x80x9d by Peterson, filed Nov. 12, 2003, a simplified control for multiphase electrically commutated motors is described. The control approach utilizes a single sensor in association with a sensible system to establish reliable phase commutation sequencing. An important result is a significant lowering of the cost of the commutation function of the motors.
Still other motor and generator (collectively referred to as electrodynamic devices) cost considerations are associated with the housings carrying electrical and mechanical components of these devices. These costs are concerned with the precise centering of bearings with respect to stator components. For instance, for some devices, the base metal plates supporting the motor or generator components can represent a predominating cost component of the completed device. Further, where adjunct modalities such as gear trains and the like are incorporated with or within the motors, their assembly in conjunction with motor construction has been observed to dramatically increase overall costs.
The present invention is addressed to electrodynamic apparatus and method of their assembly wherein a completed stator subassembly is employed as the insert in an insert molding-based assembly procedure. With this subassembly approach, a plastic encapsulation structure is developed which provides a mechanically strengthened device, while the procedures for necessary alignment of components is both simplified and improved. The stator subassembly is formed utilizing stator core members and an associated stator backiron which are integrally formed of magnetically soft pressure shaped processed ferromagnetic particles which are generally mutually insulatively associated. Over these stator cores there are positioned bobbin wound stator core windings. These windings may be interconnected in the desired winding scheme with their exit leads or lead extensions (termini) emerging from the encapsulation structure following insert molding, or as shown in the embodiment drawings, each core winding may have it""s start and finish leads (exit leads) or extensions which are supported by the bobbins emerge from the encapsulation following insert molding. The thermoplastic encapsulation structure completely surrounds these stator coils and extends radially outwardly from and within the interstices between all of the stator core components. Thus, the plastic itself enhances the dissipation of heat necessarily generated in the stator coil assemblies. Encapsulation further may additionally form the case of the motor or generator. That case, in and of itself may form the outer wall of a utilitarian device such as a power tool or the like. A particular advantage of the encapsulation approach resides in the utilization of pressed powder stator core members and backiron components in a xe2x80x9cverticalxe2x80x9d format. Because of their cylindrical structural form the insert molding process can create a feature such as gear teeth within the core structure itself yielding a very compact and much lower cost assembly than would otherwise be available with conventional assembly.
Looking at the encapsulation arrangement, bearing mounts are integrally molded with the encapsulation structure and thus, metal bearings may be press fitted within these plastic motor mounts simplifying the assembly process over mounting such devices within metal base or housing components and then assembling those components and the stator component. In the latter regard, metal base components may be eliminated to, in effect, remove what is considered one of the more expensive components of the electrodynamic devices.
In one embodiment, the plastic encapsulation structure also forms the ring gear of a planetary gear head. In this regard, the ring gear is automatically centered with respect to the bearings and the sun gear since the bearing mounts which center the bearings and the sun gear are integral to the molding tool. The result of the above features is an electrodynamic device such as a motor or generator which exhibits improved quality and importantly lower cost.
Other objects of the invention will, in part, be obvious and will, in part, appear here and after. The invention, accordingly, comprises the method and apparatus possessing the construction, combination of elements, arrangement of parts, and steps which are exemplified in the following detailed description.
For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.